Field of the Invention
The present disclosure relates to a fluoride fluorescent material and a method for producing the fluoride fluorescent material.
Description of Related Art
A light emitting diode (LED) is a semiconductor light emitting element produced from a metal compound such as gallium nitride (GaN). The semiconductor light emitting element is combined with fluorescent materials for the development of various light emitting devices that emit light of white color, bulb color, orange color and so on. These light emitting devices that emit light of white color and so on are obtained according to the principle of color mixing of light. As methods for emitting white light, a method using a light emitting element that emits ultraviolet rays and three fluorescent materials that emit light of red color (R), green color (G) and blue color (B), respectively, and a method using a light emitting element that emits light of blue color and a fluorescent material that emits light of yellow color etc. are well known. Light emitting devices adopting a method using a light emitting element that emits light of blue color and a fluorescent material that emits light of yellow color etc. are desired in a wide range of fields such as those of backlight for liquid crystals, general lighting, in-vehicle lighting and displays. Fluorescent materials to be used in light emitting devices for the application of backlight for liquid crystals, among the above-mentioned fields, are required to have not only high light-emitting efficiency but also a good color purity for reproducing a wide range of colors on chromaticity coordinates. Particularly, fluorescent materials to be used in light emitting devices for the application of backlight for a liquid crystal display are required to have compatibility of combination with color filters, and fluorescent materials having a narrow half-value width of an emission peak are desired.
For example, as red light emitting fluorescent materials having an excitation band in a blue color region and having a narrow half-value width of an emission peak, fluoride fluorescent materials having compositions of K2AlF5:Mn4+, K3AlF6:Mn4+, K3GaF6:Mn4+, Zn2AlF7:Mn4+, KIn2F7:Mn4+, K2SiF6:Mn4+, K2TiF6:Mn4+, K3ZrF7:Mn4+, Ba0.65Zr0.35F2.70:Mn4+, BaTiF6:Mn4+, K2SnF6:Mn4+, Na2TiF6:Mn4+, Na2ZrF6:Mn4+, KRbTiF6:Mn4+, K2Si0.5Ge0.5F6:Mn4+ and the like are known, and various attempts are made to improve methods for producing these fluoride fluorescent materials (see JP 2012-224536 A).